diff --git a/tests/topotests/lib/topotest.py b/tests/topotests/lib/topotest.py
index 4093c85e2d..a41350614d 100644
--- a/tests/topotests/lib/topotest.py
+++ b/tests/topotests/lib/topotest.py
@@ -58,7 +58,7 @@ class json_cmp_result(object):
         return len(self.errors) > 0
 
 
-def json_cmp(d1, d2, reason=False):
+def json_cmp(d1, d2):
     """
     JSON compare function. Receives two parameters:
     * `d1`: json value